Abstract

Wee1 is a serine/threonine kinase regulating G2/M cell cycle checkpoint through the inactivating phosphorylation of CDC2. The inhibition of Wee1 kinase by a selective chemical compound inhibitor significantly enhances the anti-tumor efficacy of DNA damaging agents specifically in p53 negative tumors by abrogating G2/M checkpoints, while normal cells with wild-type p53 are not severely damaged due to the intact function of G1 checkpoint mediated by p53 (Hirai et al, data in submission). Since measurement of mRNA expression requires a very small amount of biopsy tissue and is highly quantitative, the development of a pharmacodynamic marker leveraging mRNA expression is eagerly anticipated in order to estimate target engagement of anti-cancer agents. We here report the identification of an mRNA gene signature that was specifically induced by Wee1 inhibition in both tumor and surrogate skin tissues. In order to find the Wee1 gene signature, mRNA expression profiling was first performed in both p53-positive and -negative cancer cell lines treated with the Wee1 inhibitor. Next, to identify a Wee1 inhibitor-regulatory gene set, we carried out mRNA expression profiling of skin samples from xenograft rats given the Wee1 inhibitor. Then, the genes that were commonly modulated in both cancer cell lines and rat skin samples were extracted as the Wee1 gene signature that could potentially be used as a pharmacodynamic biomarker independent of p53 status. The expression of the Wee1 gene signature changed in a dose-dependent manner with the Wee1 inhibitor and significantly correlated with its anti-tumor efficacy. The functional features of Wee1 signature genes are also known to be related to G2/M cell cycle progression or cell cycle checkpoint, which is consistent with the mode-of-action of the Wee1 inhibitor as a G2/M cell cycle checkpoint abrogator. Given the common regulation of expression in both xenograft tumors and animal skin samples, the data suggest that the Wee1 gene signature could be used as a quantitative pharmacodynamic biomarker in both tumor and surrogate tissues, such as plucked human hair, in clinical trials.